Dirty pictures are hot. And not just for congressmen. The FBI is investigating a ring of hackers for leaking nude photos of Vanessa Hudgens, Scarlett Johansson and Miley Cyrus. Now websites are posting shots that may or may not be a buff Blake Lively. While you may sympathize with these “accidental” releases, it makes you wonder — why do they all have nude pictures of themselves in the first place?

Because, at least since the advent of the 4-megapixel camera around 2001, the privacy of bathroom mirrors and the ease of transmission has allowed everyone to become an erotic superstar.

For JR and his friends, sending pictures is a natural extension of IMs. “You send messages you wouldn’t say face-to-face.” But there’s a difference between showing your friends and distributing the pictures. “That is not cool,” he says.

Psychotherapist Sharyn Wolf considers it the grown-up version of playing doctor — with the unfortunate bonus that pixels are forever.

“The first person to see the picture is the person who takes it,” she says. “A young girl is as excited as her boyfriend — three years ago, she didn’t have that body.”

The scandals of the stars helped take the practice mainstream. In the years from Rob Lowe to Pamela Anderson to Paris Hilton, sex tapes and self-shots went from disgrace to normalcy. “Will you play along if I send a dirty picture?” Ke$ha asks in Taio Cruz’s new single “Dirty Picture,” as she rubs her hands over her body.

There’s peer pressure as well. Previous generations of teens worried about going too far in the back of the car. Now boyfriends pressure girls to send them topless shots. “Everybody’s doing it,” they say, and if you browse the web, it certainly seems true.

For some, however, the consequences can be deadly. In 2008, Ohio teen Jesse Logan hanged herself after an ex sent nude pics of her to the school. Watching a clip of an ABC special that ran at the time, it was striking how much calmer the kids were compared to the adults.

“My boyfriend asked for it so I figured, you know, I’ll go ahead and send it,” one young girl shrugs as her mother weeps. “He said, ‘You shouldn’t have ever broken up with me.’ ”

Of course, on the flip side, other young people see these pictures as a shot at fame, freely posting them on the Internet themselves. After all, celebrities from Marilyn Monroe to Madonna weren’t hurt by nude pictures, and it was “leaked” sex tapes that made Hilton and Kim Kardashian household names.

The proliferation of online dating sites has upped the ante on sharing erotic photos. You can post a picture of your sweet face, but men tend to click on the butt shots first.

“I get lots of photos. It’s completely unabashed,” says James, a 33-year-old who’s used explicit photos of himself to arrange dates online. Though he adds, “It’s not something I think is particularly healthy.”

Whether you’re hoping to find sex or share an intimate moment with your beloved, caution is the watchword.

“Even in a long-term relationship, I’m careful,” says Corinne, 25. “If we part ways and he has nude photos of me with my face, he knows that’s something he can’t publish without repercussion. It’s a mutually agreed-upon trust.”

Which sounds more like a mutually agreed-upon blackmail, though not necessarily a bad idea.